What's behind this is that private schools don't like the way the Charity Commission interpreted the Charities Act 2006, threatening their charitable status. For example, the Charity Commission say:

"Where benefit is to a section of the public, the opportunity to benefit must not be unreasonably restricted
• by geographical or other restrictions
or
• by ability to pay any fees charged"

In 2011 the Charity Commission lost a court case, and are, or should be, revising the guidelines. But pending an appeal, they have continued to publish the disputed text, but crossed out.
Here's a BBC report of the case.

Jacques Derrida uses crossed out words to signify that they don't quite express what he means. Perhaps we could all adopt the technique.

"Dear Granny, Thanks for the lovely socks. They are just what I wanted."
"Dear Valued Customer".